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Business News/ Opinion / Online-views/  Shanthu Shantharam | The route to stopping dengue
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Shanthu Shantharam | The route to stopping dengue

The battle against mosquitoes has been going on for the better part of the last century but there has been no success in terms of lasting control

There are no known vaccines to control the fever, and thus fogging is utilized to kill the mosquito larvae. Photo:Premium
There are no known vaccines to control the fever, and thus fogging is utilized to kill the mosquito larvae. Photo:

About half the world’s population is threatened by dengue fever. In 2012 alone, some 600,000 people died of dengue. It is a serious epidemic in India, and especially in urban centres. Dengue fever is transmitted by a vector mosquito called Aedes aegypti that is recognized by the white stripes on its legs, and by the lyre pattern on its thorax. It breeds heavily in pools of stagnant water, which makes its control very difficult. The causal agent is a virus that has no direct known cure, but the only option is to eradicate the vector. The battle against mosquitoes has been going on for the better part of the last century but there has been no success in terms of lasting control. Now there are two handy tools, thanks to modern biotechnology.

The two tools of biotechnology are genetically engineered mosquitoes that are male sterile and mosquitoes infested with the bacteria Wolbachia. The bacteria prevent virus replication in the mosquitoes. The idea is to introduce swarms of A. aegypti loaded with Wolbachia, but bereft of the dengue-causing viruses to prevent the spread of the disease. Dengue fever is commonly known as “breakbone fever" because of the acute body pain it causes. The disease affects around 390 million people every year, and a large majority of the susceptible population resides in South Asia, and needless to say, the bulk of them is in India.

There are no known vaccines to control the fever. Common insecticides have become useless because of the mosquitoes developing resistance, and mosquito nets are equally useless as the mosquito feeds off human blood during the day, unlike mosquitoes that carry the malarial parasite Plasmodium, which bite at night. The Wolbachia-carrying mosquitoes are in a way immunized to prevent virus replication.

What happens when these “immunized" mosquitoes are released into the environment? They breed and pass Wolbachia on to their offspring, thereby stopping the virus’s spread. Male A. aegypti mosquitoes do not bite. It’s only the females that bite as they need a protein in human blood to produce eggs. Such a female, when it bites many people, spreads the debilitating dengue-causing virus. Wolbachia also reduces the lifespan of mosquitoes, another tactic for dengue control.

Wolbachia was discovered in the 1920s, but it is only since the 1970s that scientists have learnt more about its microbiology. It took a decade of searching by Scott O’Neill and his team at Monash University in Australia to find a species of Wolbachia that could infect the female A. aegypti. His group developed a micro-injection technique to infect the mosquitoes. It is not clear how Wolbachia prevents the dengue virus from replicating, but the bacteria consistently blocked the virus from multiplying. This observation conforms to a well-known biological principle of “cross-immunization".

A team of experts at Australia’s premier research agency CSIRO carried out a thorough environmental risk assessment of the deliberate release of infested A. aegypti, and concluded that it would present the lowest possible risk to the environment or humans. Trials are now under way in Vietnam, Indonesia and Brazil.

The other biotechnology tool is the release of genetically engineered sterile male mosquitoes, which when mated with females do not yield any progeny, thereby eradicating the mosquitoes from the region. Such sterile male mosquitoes were developed by UK-based Oxitec, which field-tested them under regulatory supervision in Malaysia and Brazil. Brazil recently gave Oxitec permission to release the engineered mosquitoes on a large scale despite protests from opponents of genetic engineering.

Oxitec has submitted an application for the release of sterile male mosquitoes in India. It is yet to be decided upon by the Genetic Engineering Approval Committee (GEAC) of the ministry of environment and forests. The tragedy in India is that dengue fever has attained epidemic proportions, but there is no cure save for drinking papaya leaf extract, the ability of which to control dengue fever remains questionable.

Though modern biotech tools are available to tackle mosquito-borne diseases, public health authorities in India have not shown any interest. As expected, environmentalists have already written a letter to GEAC urging it to disallow even field-testing of these remedies and, of course, the committee seems to be in no hurry to act to alleviate the scourge of these epidemics. India must learn a lesson from countries like Brazil and Bangladesh and show the gumption to do the right thing by its people.

Shanthu Shantharam teaches plant biotechnology and biotechnology innovation management at Iowa State University and was formerly executive director of the agricultural group of India’s Association of Biotechnology-led Enterprises. He is a former biotechnology regulator with the US department of agriculture.

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Published: 03 Jun 2015, 12:21 AM IST
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